1. Field of the Invention
This invention relates to catheters and in particular to dilatation balloon catheters, for use in the performance of percutaneous transluminal procedures including peripheral angioplasty, coronary angioplasty and valvuloplasty.
2. Description of the Prior Art
In 1977 Dr. Andreas Greuntzig first used a balloon-tipped flexible catheter to percutaneously dilatate a region of stenosis within a coronary artery of a patient with atherosclerotic heart disease. Since that time, the incidence of percutaneous transluminal coronary angioplasty has increased exponentially. Over the past six to seven years, the performance of this procedure has become routine within many major medical centers throughout the world. With the advent of improved technology and operator skill, the indications for this procedure have also increased substantially.
At the outset of a routine percutaneous transluminal coronary angioplasty procedure, a pre-shaped angioplasty guiding catheter containing a balloon catheter equipped with a flexible intra-coronary guidewire is engaged within the ostium of a coronary vessel containing the lesion to be dilatated. Once suitably engaged (within the left main or right coronary ostium), the guidewire is advanced within the lumen of the appropriate vessel and manipulated across the region of stenosis. By rotating the guidewire, which contains a slight bend within its distal aspect, the operator can control the course of the wire, selecting the appropriate coronary lumen as the wire is advanced.
Once the wire is positioned across the region of stenosis, the angioplasty dilatation balloon catheter is advanced over the guidewire and positioned across the stenotic lesion. The angioplasty is accomplished by inflating the balloon of the dilatation catheter to a high pressure, typically 6 to 10 atmospheres. Generally, 3 to 4 dilatations are required for each region of stenosis. Balloon inflation is maintained for 30 to 90 seconds during each dilatation, depending upon anatomic considerations and operator preference.
Following the final dilatation, the guidewire and balloon catheter are withdrawn leaving the guiding catheter in place. Selective coronary angiography then is performed to evaluate the cosmetic appearance of the vessel following the angioplasty and to determine the severity of the residual stenosis.
At present, the major obstacle to the performance of an angioplasty procedure involves the manipulation of the angioplasty dilatation balloon catheter across the region of stenosis within the coronary artery. The guidewire usually can be advanced across the region of stenosis with relative facility in vessels which are anatomically amenable to the performance of an angioplasty. (See FIG. 1A.) However, manipulation of the balloon catheter across the stenosis often proves difficult because the cross-sectional profile of the distal aspect of the dilatation catheter is considerably greater than the corresponding profile of the intra-coronary guidewire. Advancing the relatively large caliber angioplasty catheter within a significant stenosis commonly results in disengagement of the guiding catheter from the coronary ostium. Once the guiding catheter becomes disengaged, the shaft of the angioplasty catheter frequently prolapses within the sinus of Valsalva immediately cephalad to the aortic valve, precluding further advancement of the distal end of this catheter (see FIG. 1B). The guiding catheter disengages in this circumstance because it is moderately flexible. It must be flexible because insertion of this catheter requires that it be advanced over a guidewire up the aorta, which is relatively straight, and then over the aortic arch, which is, as the name implies, curvilinear.
To circumvent this problem, a variety of "low-profile" catheter systems have been developed including the "semi-movable," "fixed-wire" and "balloon-on-a-wire" systems. The advent of new materials and manufacturing techniques has made possible the miniaturization of "over-the-wire" systems and hence the construction of these devices with lower profiles. These "low profile" systems make possible angioplasty in circumstances previously considered unsuitable for percutaneous transluminal coronary angioplasty.
Although a variety of prior art devices exist for the performance of percutaneous transluminal angioplasty, only "over-the-wire" systems permit the performance of a catheter exchange without the need to sacrifice intra-luminal access.
U.S. Pat. No. 4,323,071 describes a conventional "over-the-wire" angioplasty dilatation balloon catheter. FIG. 2 illustrates the basic configuration of an "over-the-wire" dilatation balloon catheter. A balloon catheter of this functional class consists of a dilatation balloon that is disposed on a dual lumen catheter shaft. The inner lumen of the shaft accommodates a guidewire and functions to provide column support for the dilatation balloon. The outer lumen is continuous with the dilatation balloon and functions to conduct hydraulic pressure along the length of the device. The inner lumen is separate from the outer lumen throughout the length of the catheter.
There are several disadvantages intrinsic to the design and construction of these prior art "over-the-wire" dilatation balloon catheters. For example, the outer surface of the balloon component of prior art "over-the-wire" dilatation balloon catheters invariably contain wrinkles. The wrinkles are caused by the fact that the material used in the construction of these balloons must be relatively inelastic. The wrinkles interface with the endovascular surface of the vessel during introduction of the device within a coronary stenosis and contribute to the friction generated by the catheter during this aspect of the procedure. Additionally, these wrinkles contribute to the cross-sectional profile of the catheter, and hence, contribute to the force necessary to advance the catheter within the confines of a severe stenosis.
These wrinkles further predispose the balloon to the development of perforations. The process of introducing the balloon component of a conventional catheter across intraluminal irregularities (Y-adapter O-ring valves, catheter junctions, and atheromatous lesions) frequently results in the development of shear forces within these wrinkles that cause perforations.
A further difficulty with conventional "over-the-wire" catheters is their non-uniform profile. Typically, the cross-sectional profile of conventional "over-the-wire" dilatation balloon catheters substantially exceeds the corresponding profile of the guidewires contained therein, and the transition from one profile to the other is often abrupt. Hence, the leading edges of conventional "over-the-wire" catheters frequently catch on endovascular obstructions during the course of manipulating these catheters across critical stenoses. This circumstance commonly limits the facility with which these devices can be negotiated within the confines of severe intra-vascular obstructions.
Another disadvantage of conventional "over-the-wire" catheter systems concerns the non-uniform flexibility of such systems. The rigidity of any segment of a conventional "over-the-wire" system is a function of the intrinsic rigidity of the dilatation balloon catheter and the intrinsic rigidity of the wire contained within that segment. Conventional catheters are substantially more rigid relative to the distal components of conventional guidewires. Hence, the introduction of a conventional "over-the-wire" catheter over a guidewire imparts a significant and abrupt increase in the rigidity of the composite system. The abruptness of this change in rigidity limits the navigability of these systems within the confines of complex vascular lesions.
Attempts to miniaturize these conventional "over-the-wire" systems have resulted in several additional functional disadvantages, given the constraints imposed by current technology and material availability. For example, miniaturization has resulted in the manufacture of dilatation catheters with balloons that have lower inflation profiles relative to the previous generation of catheters. Because dilatation balloons must be constructed with materials that are inelastic, there exists a fixed relationship between the inflation and deflation profiles of these balloons. Hence, the construction of low profile conventional dilatation catheters mandates the manufacture of these devices with "low profile" balloons. These "low profile" balloons frequently prove subtherapeutic, thus mandating the use of multiple dilatation catheters of progressively larger size during the course of an angioplasty. The use of multiple catheters in the performance of an angioplasty of a single lesion contributes directly to the expense and complication rate of the procedure and is a limitation intrinsic to the design of conventional "over-the-wire" catheters.
A further disadvantage of miniaturization concerns the sub-optimal torque delivery of the guidewires contained within low profile, "over-the-wire" systems of the prior art. Typically, torque delivery or guidewire "steerability" varies directly with the profile of the mandrel contained within the guidewire. Low profile "over-the-wire" systems contain low profile guidewires that provide limited torque delivery relative to prior generation guidewires of larger profiles.